It is proposed to use X-ray and neutron diffraction single-crystal investigations in conjunction with interactive computer graphics, ab-initio quantum mechanical and empirical force-field calculations to study the following problems in carbohydrate chemistry: (1) To compare experimentally the electron density distributions at anomeric and non-anomeric carbon centers in simple carbohydrate molecules and to correlate these results with the theoretical predictions from ab-initio quantum mechanical calculations; (2) To seek to distinguish between the effects of intra- and intermolecular forces in determining the deviations from ideal conformations in sugar molecules in the crystalline state using the methods of molecular mechanics, (3) To develop a molecular mechanics program which is parameterized to fit the neutron diffraction data available from mono- and disaccharides, for use in modelling polysaccharide structures. (4) To study the stereoelectronic effects of substituting sulfur for oxygen in the ring and glycosidic positions in pyranose sugars by X-ray crystal structure analysis and by an-initio MO calculations on model compounds.